Electroacoustic device



March 24, 1953 A. L. w. WILLIAMS 2,632,634

ELECTROACOUSTIC DEVICE Filed Sept. 23, 1950 5 Sheets-Sheet l INVENTOR.ALFRED L.W. WILLIAMS ATTORN EY March 24, 1953 A. L. w. WILLIAMS2,632,634

ELECTROACOUSTIC DEVICE Filed Sept. .23, 1950 5 Sheets-Sheet 2 INVENTOR.ALFRED L.W. WILLIAMS E Q an ATTOR N EY March 24, 1953 A, w, WILLIAMS2,632,634

ELECTROA'COUSTIC DEVICE Filed Sept. 23, 1950 5 Sheets-Sheet 5 I l l mmm%32 INVENTOR. ALFRED L.W. WILLIAMS ATTORNEY March 24, 1953 A. L. w.WILLIAMS 2,632,634

ELECTROACOUSTIC DEVICE Filed Sept. 23, 1950 5 Sheets-Sheet 4 INVENTOR.ALFRED L.W. WILLIAMS ATTORNEY March 24, 1953 A. L. w. WILLIAMSELECTROACOUSTIC DEVICE 5 Sheets-Sheet 5 Filed Sept. 25, 1950 FIG. l2

INVENTOR. ALFRED |..W. WILLIAMS BY ATTORNEY Patented Mar. 24, 1953UNITED STATES PATENT OFFICE ELECTROACOUSTIC DEVICE Application September23, 1950, Serial No. 186,370

14 Claims.

This invention relates to an improved electroacoustic device, and moreparticularly to an electromechanical device for transducing fromelectrical energy to acoustic energy propagating in a fluid acousticmedium.

One form of the electro-acoustic device with which this invention isconcerned is a focused acoustic treatment device, and in a more specificform the invention involves such a device of the type in which energy isgenerated by an electromechanical transducer having a radiating elementor elements arranged in a concave surface, this transducer beingassociated with an acoustic medium for concentrating the radiated energyat a focal region determined by the shape of the concave surface.

This application is a continuation-in-part of my application for LettersPatent of the United States Serial No. 88,865, filed April 21, 1949, andassigned to the same assignee as the present invention, which issued onAugust 1, 1951, as Patent No. 2,565,159.

Numerous proposals have been made during the past several decades forhastening, retarding, or

otherwise altering the course of physical, chemical, or biologicalprocesses by the use of acoustic energy of audible or inaudiblefrequencies. Devices of this character will be referred to generally inthis application and in the appended claims as acoustic treatmentdevices, it being understood that such devices may utilize frequenciesbelow, within, or above the audible range. Ultrasonic frequenciescustomarily are used for this purpose.

Two basic problems arise with such devices, first, the problem ofobtaining suflicient useful power in the form of acoustic or ultrasonicenergy propagated through an acoustic medium, and second, the problem ofapplying such energy efficiently to large quantities of the material tobe treated.

One successful answer to the first problem has been found in focusedelectro-acoustic transducers using materials having highelectromechanical responses and having physical properties permittingeasy production of the desired shapes and favoring their use with liquidacoustic media such as water and various oils. A focusedelectromechanical device of this type is described and claimed in theaforesaid copending application Serial No. 88,865, now Patent No.2,565,159. This focused electromechanical device comprises a concavebody of electromechanically responsive polycrystalline dielectricmaterial, electroded on the concave surface and on the opposite surface.

and electrically polarized to provide a major electromechanical responsein a thickness mode of motion. Means are provided for applyingelectrical or mechanical energy and for utilizing the resultingmechanical or electrical energy with translation of acoustic energy atthe focal region. A ceramic body of barium titanate material having aconcave surface of generally spherical or cylindrical shape has beenfound particularly satisfactory for this device.

While the device just discussed has produced remarkably fine results inthe field of treatment by acoustic energy, there are limitations in thepractical size of a single body of titanate or other electromechanicallyresponsive material. Thus the total radiating area focused on the focalregion of a portion of a spherical surface, or the total radiating areaper unit length focused on the axial region of a cylindrical radiatingsurface, is limited if the radiating body is made in one piece. Attemptsto utilize a number of ultrasonic radiating elements individually havingplane or concave radiating surfaces may be unsuccessful because ofundesirable mechanical resonances set up in the radiating elementsthemselves or in the structures upon which they are mounted. Themounting structures have been found to introduce often unpredictablevariations in the resonant frequencies of the individual elementsafiixed to the structures. Resonances in undesired mechanical modes alsomay be excited even when resonant operation in another mechanical modeis to be obtained. Another factor which sometimes limits the usefulnessof large electromechanical transducers is localized heating due todielectric losses.

Further difficulties also arise frequently when it is attempted tosubject large quantities of material to the ultrasonic energy in arelatively small focal region of the treatment device. Theaforementioned copending application discloses for this purpose a smallcentral tube arranged axially within a cylindrical radiator, so thatliquid to be treated may be passed through the central tube.Alternatively solid objects may be carried for treatment along the axisof a cylindrically shaped liquid-filled transducer by mechanicalconveyor means. However, it may be desired to use spherically shapedradiating surfaces for focusing the maximum amount of ultrasonic poweron a region of a given size. The second problem, mentioned above, againarises of arranging the flow of the material to be treated in such amanner as to submit each particle of a material to the high intensityenergy in the focal region for the minimum period of time necessary toobtain the desired results of the treatment. One answer, disclosed inthe aforementioned copending application, is an acoustic lens or mirrorfor projecting the focused energy along an elongated treatment pathhaving a much larger volume than the focal region. However, even thisexpedient may result in some cases in undesirable dissipation of theavailable energy, leading to inefficient use of the apparatus.

It is an object of this invention, therefore, to provide a new andimproved electro-acoustic device which avoids one or more of thelimitations of prior such devices.

It is also an object of the invention to provide a new and improvedelectro-acoustic device arranged for the eiflcient generation ofacoustic energy and application thereof to material to be treated.

It is a further object of the invention to provide a new and improvedelectro-acoustic device for the rapid and continuous treatment of largequantities of material with acoustic energy of high intensity.

It is still another object of the invention to provide a new andimproved electro-acoustic device including titanate-type ceramicelectroacoustic radiators in contact with a liquid acoustic mediumarranged for applying high intensity acoustic energy to materials to betreated.

It is yet another object of the invention to provide a novel and usefuldevice for treating fluid materials at the focal region of a generallyspherically shaped electro-acoustic transducer or array.

In accordance with the invention, an electromechanical device fortransducing from electrical energy to acoustic energy propagating in afluid acoustic medium comprises a support member having a back surfaceand an opposed supporting surface and having numerous perforationstherethrough and acoustic pressure-releasing means affixed on one sidethereof to this supporting surface and having numerous openings at leastpartially aligned with the aforesaid perforations. The device includes aplurality of electromechanically sensitive elements, each having a backsurface, aifixed to the pressure-releasing means on the other sidethereof, and a front surface, the front surfaces collectively A formingan electro-acoustically responsive array for coupling to the fluidacoustic medium. This electromechanical transducing device furthercomprises means, including electrodes adjacent to each of theelectromechanically sensitive elements and a system of leads connectedto the electrodes, for applying electrical energy to theelectro-acoustically responsive array, and the transducing device alsois arranged for motion of the fluid acoustic medium from the backsurface of the support member through the perforations and past theelements during operation of the device.

In accordance with another feature of the invention, a focused acoustictreatment device comprises electromechanical transducing means fordirecting acoustic energy from an electroacoustically responsiveradiator of sizable area toward a focal region having high acousticenergy intensity, having a relatively small effective area, and having acorrespondingly small volume, This device also comprises a liquidacoustic transmission medium in contact with the radiator, a solidacoustic-energy-transmitting barrier remote from the radiator andseparating the liquid 4 medium from the focal region, and means fordirecting a flow of material to be treated into the device and throughthe focal region of small volume to subject substantially all of thematerial in the flow expeditiously to the acoustic energy of highintensity.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

In the drawings,

Fig. 1 is a sectional view in elevation of an electro-acoustic device inaccordance with the present invention, certain portions of the hydraulicarrangements in the device being illustrated schematically;

Fig. 2 is a perspective view of the electromechanical transducerarrangement incorporated in the device of Fig. 1 showing for simplicityof illustration only a small fraction of the total number of transducerelements actually present in the transducer arrangement;

Fig. 3 is a sectional elevation of a portion of the transducerillustratedin Fig. 2, showing the construction of the transducerelements and the supporting structure;

Fig. 4 is a sectional elevation of an alternative form of theelectro-acoustic device of Fig. 1;

Fig. 5 is a sectional elevation of an alternative arrangement for thetreatment head incorporated at the top of the device illustrated in Fi4;

Figs. 6 and 7 are sectionalized elevation and plan views respectively ofanother form of treatment headwhich may be incorporated in the Fig. 4device;

Figs. 8 and 9 are. sectionalized elevation and plan views respectivelyof a further alternative arrangement of the treatment head;

Figs. 10 and 11 represent still other forms of the treatment head; and

Fig. 12 is a sectional elevation of another embodiment of a focusedacoustic device, alternative to the forms of electro-acoustic devicesshown in Figs. 1 and 4.

Referring to, Fig. 1 of the drawings, there is shown in sectionalelevation an electromechanical device, embodying the present invention,for transducing from electrical energy to acoustic energy propagating ina fluid acoustic medium. The electromechanical device shown in Fig. l isa horizontally disposed focused treatment device. The major portions ofthis device may be identified at the outset as a base casting H, asupport member 13 for supporting, a plurality of electromechanicallysensitive elements !5-, l8, ll, etc., a housing 19, and a hydraulicsystem including a fluid acoustic medium, preferably in the form of aliquid medium '21, which convenient- 1 may be castor oil. A treatmenthead 23 is attached to, and forms a removable part of, the housing [9remote from the base i I. This housing also is provided with a wallportion 25 adapted to transmit acoustic energy while confining theliquid Zl so that it cannot enter the treatment head 23.

The base II and housing l9 may be castings of any suitable material,such, as stainless steel, brass, or aluminum. The housing 19 is shown inthe shape of a truncated cone with a flange around the wider end. Thebase H is concave inwardly and has the shape of a portion of a sphericalsurface; a major chord across the rim of this surface convenientlysubtends an angle of some 70-80". A suitable radial dimension for thisspherical surface may be about 14 inches. The spherical portion of thebase I I is surrounded by a rim having a flat surface for fastening tothe flange of the housing I9. A circular indentation is provided in thisrim of the base I I for receiving a gasket ring 21, which is compressedwhen the flange of the housing I9 is pulled against the base by means ofbolts 23, 29 to provide a seal which is tight against the liquid 2|under pressure.

The treatment head 23 is hollow and open at one end. This end is flangedto fit against a flattened surface provided at the smaller truncated endof the conical housing I9. This flattened surface also is provided witha circular indentation into which is fitted another gasket ring 3i. Thehead 23 is secured to the smaller end of the housing I9 by means ofbolts 32, 33 which compress the gasket ring 3I to provide a liquidtightseal. The acoustic-energy-transmitting portion or acoustic window 25 iscurved and also has the shape of a portion of a sphere. The window 25 iscemented into a circular recess provided in the walls of the head 23 atthe open end thereof with the concave surface of the window facing theinterior of the head 23. The curvature of the window 25 is adjusted sothat, when assembled, its center of curvature approximately coincideswith the center of curvature of the spherical portion of the base II,this center of curvature being near the center of the interior of thehead 23.

The entire assembly may be maintained with the central radius of thespherical surface of the base II in a horizontal position by means ofbrackets 36 and 3'! affixed to one or more of the bolts 28, 29 and 32,33 respectively.

The support member I3 and the electromechanically sensitive elements l5,I6, etc. are parts of an electromechanical transducing means fordirecting acoustic energy from an electroacoustically responsiveradiator of sizable area, made up of the elements I5, I6, etc., toward afocal region having high acoustic intensity, having a relatively smalleffective area, and having a correspondingly small volume. Such a focalregion is formed within the head 23 in the neighborhood of the center ofcurvature of the base II. At least the convex back surface of thesupport member I3 is electrically conductive. The entire support l3suitably may be of heavy copper sheet cut into a disk and formed into adished shape having the same center of curvature as the concave portionof the base II. The sheet material forming the support has numerousperforations therethrough. The support I3 is affixed to the housingassembly by screws 34, 35 threaded into tapped holes in a raised portionof the base II just inside the outer flange of the base. The assembly ofthe support I3 to the base II is further stiffened by a number of bosses38, 39 protruding from the concave surface of the base I I.

More detailed views of the support I3 and the electromechanicallyresponsive elements carried by it are found in Figs. 2 and 3. Thesupporting structure is seen in Fig. 2 to have a great many rather smallperforations, and several of these perforations GI, 42, 43, etc. areseen in the sectional view of Fig. 3. It is advantageous to place asufiicient number of electromechanically r sponsive elements on thesupport I3 so that in effect the concave surface which is opposed to theconvex back surface of the support member and is the supporting surface,is practically covered by these elements. However, it is convenient toleave an uncovered space near the edge of the support, and a practicalcomprise utilizes six standoff insulators 44-43 arranged around thesupport near the rim thereof at re ularly spaced intervals, that is, atthe corners of a regular hexagon. Rather heavy copper bus bars or wiresare strung all around the support between successive insulators 44-49,and lateral wires are arranged in roughly parallel lines, but conformingto the dished shape of the support, between suitable ones of these outerbus bars. Two such lateral wires 5|, 52 are shown by way of example inFig. 2. A number of the electromechanically responsive elements also areshown in Fig. 2. These elements are hexagonal in cross section. Thehexagonal shape permits easy assembly of large numbers of the elementson a curved surface with closer packing or utilization of the area thanmay be obtained with other shapes.

The manner of assembly of the sensitive elements I5, I6, I'I, etc. onthe support I3 and their electrical connections are illustrated in Fig.3, showing elements I5, I6, I'I, etc. Only a portion of one row of theelements is illustrated, the method of packing the elements on thesupport being illustrated for one representative portion of thetransducer means by the group of elements shown in Fig. 2.

Before arranging the sensitive elements on the support I3, an acousticpressure-releasing means is amxed on one side thereof to the concavesupporting surface of the support I3. The pressure-releasing means hasnumerous openings at least partially aligned with the perforations inthe support I 3. Thus this means may be in sheet form with holes punchedthrough the sheet for alignment with the perforation. However, at leastwhen only small quantities are involved, it has been found moreconvenient to stamp out a separate pressure-releasing pad 54 for each ofthe sensitive elements as seen in Fig. 3. These pads may have the samehexagonal shape as the elements themselves. The acousticpressure-releasing means serves to decouple the elements from thesupport member and in general may be any material or structure a sizableportion of which may suifer small compressions without exerting ortransmitting substantial pressures. A suitable composition is made up ofparticles of cork and synthetic rubber, affording an effectivelycellular structure.

With the pressure-releasing sheet or pads 54 affixed on one side thereofto the support I3, the back surface of each of the sensitive elements isaffixed to the support I3 on the other side of the sheet or pads, asshown in Fig. 3. It may be convenient, when numerous separate pads 54are used, to cement the pads to the elements first and then to cementthe elements to the supporting surface. The spaces between the elementsand their pads then fall into alignment more or less randomly withportions of many of the perforations in the support.

Each element has a front surface on the end or side of the elementopposite from the mounted or back surface. These front surfacescollectively form an acoustically responsive array for coupling to theacoustic medium 2I. As viewed in Fig. 1, this array is directed towardthe acoustic-energy-transmitting wall portion 25 of the housingarrangement. More specifically, the

front surfaces of the elements fall on an imaginary spherical surfacehaving substantially the same center of curvatureas the concave innersurface of the base I of the mounting arrangement.

The electromechanically sensitive elements |5, |5, etc. may be of any ofnumerous piezoelectric materials such as quartz, Rochelle salt, andammonium dihydrogen phosphate. None of the materials just mentioned isideal. Forming elements of a hexagonal cross-sectional shape fromsingle-crystalline material increases the cost of the device. Thequartz, although not subject to physical or chemical attack by manysubstances which might be used for the fluid acoustic medium, isexpensive and has relatively low piezoelectric sensitivity. Many of theother piezoelectric materials having higher sensitivities are dissolvedor otherwise deteriorated in contact with various fluids, and aresubject to rather stringent temperature limitations. When the liquidacoustic medium is an aqueous one, watersoluble crystals would have tobe covered by an impervious moisture-sealing coating.

It is preferred to fashion the elements of polycrystalline titanate-typematerial. Such elements may be formed inexpensively by an extrusionprocess when the ceramic material is in the raw state, followed byceramic firing. The extruded hexagonal rods are cut to the desiredlength after firing. These elements are mechanically strong, unless verylong, and are waterinsoluble. A barium titanate composition ispreferred. For resonant operation at a single frequency of the acousticvibrations, the elements should be cut to a length corresponding to halfof the wavelength of longitudinal compressional acoustic waves of thedesired frequency in the polycrystalline material.

Means are provided, including electrodes adjacent to each of theelements and a system of leads connected to the electrodes, for applyingelectrical energy to the electro-acoustically re- :sponsive array formedby the elements. Electrode means are arranged adjacent to two opposedsurfaces of each. of the elements. :in Fig. 3, electrodes 56 are placedadjacent to :the back surface and electrodes 51 are placed adjacent tothe front surface of each of the elements,

Thus, as shown support member |3 with the electrodes 56 adja cent to theback surfaces of the elements. Lead means now can be arranged inproximity to the front surface of the elements and interconnecting theelectrodes 5'! adjacent to thesefront surfaces. Such lead. meansincludes wires or straps 59 connecting each electrode 51 with thenearest one of the lateral wires 5|, 52, etc., or with one of the busbars strung between the insulators 44-49, as shown in Figs. 2 and 3.

An external source of high power ultrasonic frequency electrical energy,not shown, is connected to the device by means of a suitable twoconductor cable 6|. One conductor of this cable is grounded to thehousing. i9 at a lug 62, as shown in Fig; l. The other conductor passesthrough a water-tight fitting G3 and an insulating sleeve 64 to aninternal bus 66, which in turn is connected to the aforementioned busbars and lateral wires 5|, 52, etc., leading to each of the frontelectrodes 51. The back electrodes 56 are returned to ground throughtheir leads 58, the copper support It, and the metallic housing IS. Thearrangement of the fitting $3, the conductor 65, and the ground returnpath from the support l3 to the lug 52 furnishes a terminal-circuitmeans for applying electrical energy from the generator across the leadconductors 58 and the lead means which includes the lateral conductors5|, 52 and the leads 51, and thus across the electrodes on each of theelements.

Numerous other arrangements of the lead conductors and lead means, ofcourse, may be used. For example, the lead means connected to the frontelectrodes 5! might utilize lateral conductors 5|, 52 of flat or ribbonshape; if the elements are not too closely spaced, such thin conductorsmight be arranged to fit between the elements instead of above theradiating surface of the array. However, when the elements are of atitanate-type material, these elements ordinarily are subjected to ahigh unidirectional polarizing voltage before the ultrasonic frequencygenerator is connected to them. This polarizing treatment provides ahigh sensitivity and a linear response. Moreover, it is desirable insome cases, particularly after the elements have been subjected to highelectric fields or high temperatures, to repolarize them while stillmounted on the support 13 and Wired to the leads 58 and 59. In suchcases short-circuiting might occur between the back electrodes 55 andthe lead conductors connected to the front electrodes 51 if these leadconductors are placed between the elements rather than above them. Itmay also be mentioned that it is desirable to maintain a spacingbetweenthe sides of adjacent elements of the order of 0.050 inch to preventunwanted or destructive acoustic forces from acting on a very narrowbody or thin film of liquid between the sides of adjacent elements. Suchforces may arise from the lateral motion of the elements which occurssimultaneously with changes in the dimension between the back and frontelectrodes.

The transducing device is arranged for motion of the fluid acousticmedium 21' from the back surface of the support member |T3' through theperforations ll, 42, etc. and past the elements i5, Hi, etc. duringoperation of the device. This motion may be due merely to convection currents caused by heating of the medium 2| as a result of temperaturerises occurring in the elements themselves during transducing. Suchconvection circulation will be mentioned hereinbelow in connection withthe device illustrated in- Fig. 4.

In the Fig. 1 arrangement there is provided liquid-guiding means fordirecting a flow of the liquid acoustic medium at a substantial velocitythrough the perforations, past the elements within the housing I9 towardthe Wall portion '25 thereof, and thence generally lateral of this wallportion to establish a continuous acoustic path through the movingliquid medium 2| between the array of sensitive elements and thea-coustic-energy-transmitting wall portion 25'. This liquid-guidingmeans includes a liquid inlet fitting 68 for admitting liquid to thespace between the base II and the support l3; and a conical baffle 69for guiding the liquid passing through the perforations in the directionof the 9 wall portion 25. The baflie 69 is flanged at its wider end andaffixed as by soldering or welding to the supporting surface of thesupport I3.

The back surface of the support l3 just behind the flange of the bafile69 is in contact with a compressible ring-shaped gasket 7|, so that thebafile and this gasket prevent any substantial flow of liquid alongeither the back surface or the supporting surface of the support mem-'ber I3 from the central portion of the support, Where the elements l5,l6, etc. are mounted to the outer portion of the support. This outerportion, however, also is perforated to permit passage of liquid fromthe space between the bafiie 69 and the housing I!) to the annular space12 bounded by the gasket 7|, the base II, the raised portion of the baseto which the support It is screwed, and the outer portion of thesupport. Liquid can leave this annular space 12 through a fitting 13.

In addition to the liquid-guiding function of the baffle 69 and thegasket 1|, the liquid-guiding means may include an external arrangementfor circulating the liquid medium and returning it to the back surfaceof the support member I3. A hydraulic system for efiecting thecirculation is illustrated schematically in Fig. 1. Liquid leavingthrough the fitting 13 passes through piping 14 to a pressure reliefvalve 16 and thence into the upper portion of a chamber 11. The chamber11 is only partially filled with the liquid, and its upper portion isconnected to a vacuum pump 18 for continuously degassing the liquidmedium. The degassed liquid passes from the bottom of the chamber 11through piping 8|] to a pressure pump 19, which pumps the liquid into apressure-regulating device 3| and thence back to the fitting 68 and intothe space behind the central portion of the support I3. The piping l4and 8B is shown broken in Fig. 1 to indicate that a sufficienthydrostatic head may be maintained in vertical portions of this pipingto permit flow of liquid from the evacuated chamber TI to the inlet endof the pump '19. This pump serves as a means for maintaining thecirculating liquid medium 2|, acoustically coupled to the arrayelements, under a substantial hydrostatic pressure while between thearray and the acousticenergy-transmitting wall portion 25. If desired afine-meshed filter also may be inserted in the circulation system toremove any small solid impurities from the liquid medium, since suchimpurities may serve as nuclei supporting unwanted cavitation in theliquid medium during operation of the device.

Means for controlling the temperature of the circulating liquid mediumis provided in the form of an annular channel 33 in the wall of thehousing I9 near the narrower end of the housing. As seen in Fig. 1,there is a cooling water inlet 84 threaded to receive a cooling waterconneotion and communicating with one end of the channel 83. The channelmakes almost a complete circle within the walls of the housing I9, andan outlet connection, not visible in Fig. 1 'but similar to the inletconnection 84, also communicates with the channel not far removed fromthe connection 84. The channel is closed between the inlet and outletconnections to permit circulation around almost the entire periphery ofthe wall. It is noted that for operation under cold ambient conditionsthe liquid circulated through the channel 83, instead of .being acoolant, :might be warmer than the housing I9. In either case heat istransferred between the liquid 2| and the liquid in the channel 83through the walls of the channel so as to exert control over thetemperature of the liquid medium 2|. Since the liquid 2| is in contactwith the elements l5, l6, etc., the liquid 2| serves not only as anacoustic medium but also as a heat-transfer medium to prevent extremesof the temperature of the elements.

It will be seen from Fig. 1 that the liquid 2| is an acoustictransmission medium in contact with the electro-acoustically responsiveradiator made up of the elements l5, l6, etc. The housing for thisradiator and for the liquid medium 2| contains therein wall portion 25,which forms a solid acoustic-energy-transmitting barrier remote from theradiator and separating the liquid medium 2| from the focal regionwithin the head 23. The pump 19 constitutes means for maintaining theliquid medium 2| under a substantial hydrostatic pressure within thehousing and contiguous to one side of the barrier 25, that is, to theleft side as seen in Fig. 1.

Referring now more particularly to the treatment head 23 the headincludes means for directing a flow of material to be treated into thedevice and through the focal region of small volume within the head tosubject substantially all of the material in the flow expeditiously tothe acoustic energy of high intensity developed in the focal region.Ordinarily the material to be treated is a liquid material, but thisliquid may contain suspended or dispersed solids, or the liquid materialmay be a mixture of moderately small droplets of two or more ordinarilyimmiscible liquids. Alternatively two liquids to be mixed may beintroduced into the head through separate passages.

The end of the head 23 remote from the barrier 25 is threaded to receivea hollow cylindrical member 86, which is sealed against a shoulder inthe head '23 by a gasket 81. The other end of the cylinder 86 isthreaded to receive a plug 88 having a central hole through which passesa pipe 89. The pipe 89 is sealed within the cylinder at the end of theplug 88 by a cap 9|, which threads on a threaded extension of the plug88 so as to squeeze a gasket 92 against the plug 88 and the wall of thepipe 89. Thus an annular channel 93 is formed between the inside wall ofthe cylinder 86 and the outside wall of the pipe 89. An inlet pipe 94through the wall of the cylinder 86 communicates with this annularchannel 93. The end of the pipe 85 within the head 23 is flared toencompass the focal region of high acoustic energy intensity in theneighborhood of the center of curvature of the electro-acoustic array.The pipe 89 may be adjusted longitudinally while the cap 9| is loose sothat the flared portion has the desired close relationship to the regionof most intensive acoustic activity.

An auxiliary inlet tube 95 passes through one side of the wall of thehead 23 to the end of the head near the barrier 25, where it makes a Uturn so that its end is near, and points into, the flared end of thepipe 89. Gasses entrapped within the head 23 may be bled out through aplugged hole 9'5. When the device is not in operation, the liquid may bedrained from the head 23 through a plugged hole 98. Another plug 99 inthe base interior of the housing for cleaning purposes.

In preparing the device shown in Fi 1 for operation, the interior of thehousing I9 is filled with the liquid 2| and the pumps 18 and 19 are setin operation, The pressure-regulating device 8! and the pressure reliefvalve 16 are adjusted for stable operation of the circulating systemunder the desired hydrostatic pressure. The liquid medium 21 enteringthrough the fittin 6 is distributed within the space between the base I!and the support 13, this space being enclosed within the gasket II. Theliquid then passes through the perforations in the support l3 to thebarrier 25, where it reverses its direction of flow to return outside ofthe baffle 69 to the space 72 near the flange of the base II and thenceout through the fitting I3. Circulation is continued for a sufficientlength of time to permit the liquid 2| to be thoroughly degassed throughthe operation of the vacuum pump 18.

The material to be treated is fed through the pipe 94 and the annularspace 93 into the interior of the head 23. The plug 9'! may be removeduntil this material flows out, at which time the treatment head has beenfilled with liquid and the plug is replaced. The treated material flowsout through the pipe 89, which has suitable outlet valves, not shown, tocontrol the rate of flow.

This completes the course of flow of the material to be treated if thetreatment is an opera tion affecting the course of chemical or biological processes in a single body of liquid. Similarly, the flow path justdescribed is suitable for an operation, such as the sterilization oragglomeration of a single liquid or of a liquid dispersion, or if twoliquids to be emulsified are pre-mixed and fed together through theinlet 96. In some emulsifying operations, however, it is preferable tointroduce one of the liquids separately. As an example, an aqueous.material may flow in through the tube 96 for mixing with an oily liquidintroduced through the inlet pipe 94.

The ultrasonic frequency generator now is connected operatively to theelements l5, l6, etc. through the cable 6!. Electrical energy istransduced into ultrasonic frequency acoustic energy originating at theelectroded front surfaces of the array of elements, and the acousticenergy propagates toward the focal region and passes with littlereflection or absorption through the barrier 25 when there is liquid onboth sides of the barrier. This barrier may have a thickness equal toone half of the wave length of the ultrasonic energy at the chosenfrequency, dependin upon the velocity of propagation of the energythrough the metal barrier. For a frequency of 100 kilocycles per secondthis thickness is about two thirds of an inch in brass. Such a half wavebarrier sets up reflections of pressure waves without phase reversal atthe first or liquid solid interface and with. phase reversal at thesecond oi solid-liquid interface. These two reflections remain out ofphase and tend to cancel in the liquid medium 2| because the total roundtrip path between the two interfaces is one wave length. Therefore mostof the energy radiated from the array passes through the wall portion 25to the focal region. The curved shape of the wall 25 conforms to thedirection of propagation of the wave fronts originating at the focusingarray, so that the wall 25 has the same effect on the acoustic energyoriginating from each element of the array, and so that any energyreflected back is distributed over the entire array and not concentratedon one part of it.

At the frequency just mentioned, the electromechanically sensitiveelements Of barium. titans 12 ate ceramic material exhibit lengthresonance when about three quarters of an inch long. Resonant operationordinarily is desired to obtain the highest levels of acoustic energyand sensitivity. It is important that each of the elements I 5, it, etc.be resonant at the same frequency, since small deviations from resonancein either direction may cause serious phase shifts. Thus, if one elementis driven slightly below and an- I other element slightly above theirresonant frequencies, the radiation from the two elements may in greatpart cancel.

It has been found to be important, moreover, that the several elementsnot only be of equal efiective lengths but also be maintained at roughlythe same temperature. This results from the fact that, at least withincertain temperature ranges, various electromechanically sensitivematerials exhibit substantial changes of the resonant frequency withchanges in temperature of an element having given dimensions. Thus forexample, if one group of elements becomes cooler than, and another grouof elements becomes warmer than, the remaining elements, these twogroups may be effectively detuned in different directions and this mayupset seriously the focusing action of the array. Such effects may bepaticularly troublesome if the apparatus is mounted with its axishorizontally, as in Fig. 1, due to the considerable vertical distancebetween the uppermost and lowermost elements. Dielectric losses in theelements cause the medium 29 to become heated, and hotter liquid tendsto stratify in the upper portions of the housing near the uppermostelements while cooler liquid tends to fall toward the drain plug 99.This difiiculty is avoided in the Fig. 1 arrangement by the forcedcirculation of the medium 2|. Furthermore, for certain titanate-typeceramic elements, optimum operation occurs in the temperature rangebetween room tmeperature and about or C. Accordingly, it is not alwaysenough to maintain the temperature of the medium 2| uniform, and coolingwater is circulated through the channel 83 to perform the additionalfunction of maintaining all of the liquid cool enough so that theelements [5, [6, etc. do not become hotter than about 90 C. Bariumtitanate elements have additional advantages for resonant operation whenthe elements are at temperatures in the neighborhood of 70 0., sincebetween 50 and 90 C. they exhibit only slight changes of resonantfrequency with changes in temperature. In addition, these ceramicelements are less critical with respect to frequency than are somepiezoelectric elements since the titanate-type elements in contact withliquids exhibit a somewhat less sharp resonance characteristic.

Referring again to the treatment head 23, it will be apparent that theconcentric arrangement of the inflow and outflow paths of the materialto be treated tends to direct the flow of this material steadily,expeditiously, and without the formation of stagnant pools of thematerial through the focal region within the flared end of the pipe 89.Since there is no other path for the material to travel except throughthis focal region, substantially all of the material is subjected to theacoustic energy in the focal region. The rate of flow of the material tobe treated is adjusted until the desired efiects of the treatment areobtained at about the highest possible rate of flow. In most cases thisadjustment is such as to obtain cavitation in the liquid to be treatedin a small region within the flared end of the pipe 89.

While both operations would be possible within a small treatment head,the advantages of an arrangement for continuous passage of material tobe treated through a head such as the head 23 are obvious. A very widevariety of treatment operations is practical. Suspensions ordispersions, colloidal or otherwise, in fluid media may be treated. Thefunctions of a colloid mill are performed more speedily andinexpensively. Very stable emulsions can be formed. The particles in acopper powder, as an example, may be disrupted and very finely dispersedin a liquid of low or high viscosity. Almost endless variations of suchtreatments are available to one skilled in the art of acoustic treatmentusing the device of the present invention.

The discussion hereinabove concerning the importance of a uniformnatural resonant frequency for each radiating element illustrates thenecessity of decoupling the electroded back surfaces of the array ofelements from the supporting surface of the support member I3. Thepressure-releasing material 54 between the surfaces provides aneffectively free or unclamped acoustic termination for the backs of theelements. If it is attempted to mount or clamp the elements directly toa solid supporting structure, an effective distance approximately equalto the thickness of this structure is added to the length of eachelement provided the supporting surface is affixed firmly to the elementat every minute portion of the back surface thereof. This is difiicultto achieve, however, and very small areas improperly cemented orcontaining voids can have a profound effect on the resonant frequency ofthe element involved. This not only upsets the focal pattern but alsomay lead to destructive acoustic forces at the interface, particularlyif the acoustic medium can penetrate behind the element.

Other deleterious effects which may result from attempting to coupleeach element acoustically to a single stiff backing or support arisefrom the lateral motion occurring in the elements by piezoelectric orelastic coupling to the longitudinal vibrations. This unwanted coupledlateral motion may cause losses in the dielectric or may cause drasticmodifications of the resonant characteristics of the elements. Ifextremely large lateral dimensions, in terms of the wavelength in theelectromechanically sensitive material, can be obtained, the effects ofsuch lateral resonances on the response in the longitudinal mode may beavoided. However, for spherical radiating surfaces having areas of theorder of, say, 70 square inches it may be impractical to fabricate atitanate bowl-shaped radiator in one piece. If it is attempted to makeup the desired area using, for example, eight or a dozen separateradiators having concave surfaces, the lateral dimensions of each suchelement are likely to fall within the range in which unwanted resonancesoccur, since the lateral dimensions may be about three or four times thehalf-wave longitudinal or thickness dimension. These difficulties areavoided by making the lateral dimensions small compared with a half wavelength, for example about a half inch maximum for barium titanateceramic material at 100 kilocycles per second, and including asufficient number of elements to obtain the desired radiating area. Inthe case of the device illustrated in Figs. 1 and 2, about 350 separateelements were used.

Referring now to the modified arrangement illustrated in Fig. 4, it isseen that the housing is similar to that shown in the Fig. 1arrangement,

except that the walls are thinner. Only somewhat elevated internalpressures are employed with the Fig. 4 device. Portions of this devicewhich are the same as portions of the Fig. 1 device are indicated by thesame reference numerals, while similar portions are indicated by thesame reference numerals primed.

Thus, the Fig. 4 device has a base II and has a support I3, which isfastened to the base by screws 34, 35 at the periphery of the supportand which is braced additionally by bosses 38, 39. The device furtherincludes elements I5, I6, I1, etc., supported on the support I3 just asillustrated in Figs. 2 and 3 but with the elements filling thesupporting surface to the extent that only a narrow margin is left freeof the elements around the edge of the support. The housing I9 isfastened to the base I I by bolts 28 and 29, and a gasket 21 makes thejoint tight.

It will be noted particularly that the Fig. 4 device is illustrated foroperation with its axis vertical rather than horizontal. The liquidmedium 2I within the housing may be drained or filled through a plug 99'at the center of the base I I. When the housing has been filled, theliquid medium passes through a channel Iill into an expansion orpressure chamber I02 having a plug I03. This pressure chamber has aninternal volume which increases as the liquid 2| expands from heatingduring operation, and the increased volume may be made to cause thechamber I02 to exert a predetermined hydrostatic pressure on the medium25. The liquid 2| is degassed before introduction into the housing l9,but any vapor which might develop Within the housing during operationcan be purged through the plug I03 in the chamber I02.

The cable GI brings electrical energy to a lug 62 grounded to thehousing I9 and also through a pressure-tight feed-through fitting 63' tothe internal bus conductor 66.

During operation of the Fig. 4 device the liquid 2i is heated as aresult of dissipation of energy within the dielectric material of thesensitive elements. This heating causes a convection flow to be set upwithin the liquid 2| from the Warmer portions of the array upward andthen back downward toward the cooler elements. This circulation isimproved and made more effective for cooling the lower portions of theelements by virtue of the perforations in the support I3, since thecirculating medium can pass through some of these perforations and thenflow laterally in the space between the base I I and the support I3 toemerge through other perforations in the neighborhood of the warmerelements. With the array in the vertical position illustrated theconvection currents are facilitated, and any variations in temperatureof the elements tend to be small and to be symmetrical with respect tothe axis of the device, so that such variations have a negligible effectupon the focusing action of the array.

Undesirably high temperatures of the elements and hence of the medium 2iare avoided by introducing cooling water through a pipe I04 into areservoir I06 surrounding the upper part of the conical housing I9. Auniform narrow space is maintained between the bottom of the reservoirI06 and the outer wall of the housing I9 by suitable brackets, notvisible in Fig. 4, and the cooling water flows downwardly through thisspace all around the housing. The cooling water flows smoothly down theouter surfaces of the housing I 9, as indicated by the arrows in Fig. 4,and the water passes over the flange at the bottom ofthe housing I9after it has served its purpose.

The treatment head and solid barrier in the Fig. 4 device are ofdifferent design from those illustrated in Fig. l. The head I II isfastened to the main portion of the housing I9 by bolts 32 and 33. Adiaphragm II 2 in the shape of a disk having a diameter equal to theouter diameter of the head III is interposed between the head and thehousing proper. A gasket ring 3I insures a tight seal between thediaphragm and the housing, while a washer I I3 forms a seal between thediaphragm and the head.

The focal region within the head is located just beneath the upper wallN4 of the head. This wall has a thickness equal to a quarter wave lengthfor the material of the wall at the frequency of operation. For example,at 100 kilocycles per second this thickness is about one third of aninch for brass and about a half inch for aluminum. This makes the wallIII an efficient reflector of acoustic energy and thus enhances theintensity of the energy in the space just below the wall I I I when thehead I I I is filled with an acoustic medium. This medium in the form ofa liquid material to be treated may be introduced through a duct I I6just to the left of the focal region and the treated material then isremoved through a duct In just to the right of the focal region, asviewed in Fig. 4. This liquid material fills the space between the topII4 of the head and the diaphragm H2. The diaphragm may be of stainlesssteel about ten thousandths of an inch thick.

If it is desired to emulsify a small amount of one liquid in a largeamount of another, the two liquids may be introduced separately. Thus alarge amount of water may be introduced into the head through anauxiliary duct IIB entering the interior of the head well below thefocal region. A relatively small amount of oil, introduced through theduct H6, floats on the water just beneath the top I I4 until it isemulsified with the water, and the resulting emulsion is removed throughthe duct I I I.

Alternative arrangements of the treatment head, suitable forsubstitution for the head II I in the Fig. 4 device, are shown in Figs.5-11, inclusive. Referring to the sectional view of Fig. 5, there may beseen the diaphragm IIZ, the sealing washer I I3, and the head proper I II having a reflecting quarter wave upper wall IM, an entrance duct I I6,an exit duct I I1, and an auxiliary entrance duct H8. The head IIIdiiTers from the head III, shown in Fig. 4, in that the quarter waveupper wall portion II4 is flat, whereas the wall I I4 in Fig. 4 iscurved to minimize any tendency of reflected energy which might passthrough the treatment region to be concentrated through a limited areain the middle of the diaphragm II2. While the upper wall portion H4 ofthe head III is not curved, the lower surface of the wall H4 iscorrugated by a number of channels I I 9, I20, etc. These channels runcross-wise of the direction of flow of the liquid material entering andleaving through the ducts H6 and III. The wall portion II I' may be aquarter wave in thickness between the channels, while the channelsthemselves may have a depth about one tenth of this dimension.

In the operation of the Fig. 4 device when equipped with the head shownin Fig. 5, the liquid material being treated flows into and out of eachcorrugation, providing an elongated treatment path in the focal region.Any reflected energy which might penetrate back to- 16 ward the radiatortends to be well scattered. This type of head is designed for use wherethe acoustic treatment occurs principally in a rather thin film ofliquid; the corrugations II9, I20, etc. provide a larger eifectivesurface for treatment of the liquid film.

Figs. 6 and 7 are sectional views illustrating in elevation and planrespectively another type of treatment head I2I. The view of Fig. '7 istaken in the direction indicated by the arrows I, I in Fig. 6. Thediaphragm H2 and washer II3 are the same as with the head III of Fig. 4.The head I'EI has a flat upper wall I22 which is a quarter of a wavelength in thickness. An inlet duct I23 for the material to be treatedends in a flared portion In, which aids in distributing the materialover the upper half of the interior of the head I2 I. An outlet duct I26likewise has a flared entrance I21 for collecting the treated materialfrom the upper half of the interior of the head. The acoustic energypassing to and reflected from the wall I22 also meets a group of thinbaiile disks I23, I29, and I38, which have been pressed into grooves inthe front and rear interior walls of the head. The material beingtreated passes not only between the wall I22 and the baflle I 28, butalso through the two spaces between the baflles and beneath the baflleI30.

The head arrangement of Figs. 6 and 7 affords four separate treatmentareas, thus providing a greatly increased effective volume. Thisarrangement is designed for treatment of materials which do not requireviolent cavitation during treatment and which are to be treated inrather thin films. The bafile disks I28, I29, and ISO may be ofstainless steel about five thousandths of an inch thick and separated bymuch less than a quarter wave length in the liquid to be treated. Asuitable spacing of the disks at the frequency mentioned hereinabove isabout an eighth of an inch for most liquids.

Figs. 8 and 9 show another alternative treatment head I3I, Fig. 8 beinga sectional elevation and Fig. 9 a sectional plan view taken in thedirection indicated by the arrows 9, 9 in Fig. 8. In this case thebaffle H2 and, if desired, the sealing ring 3! are omitted from the Fig.4 assembly, leaving the washer II3 to seal the head I3I to the housingI9. Again the head has a quarter wave upper wall I32. Around the edge ofthe interior surface this wall is a slightly raised ledge I33 againstwhich is secured a diaphragm disk I345. The inlet and outlet ducts inthis head pass vertically through the upper wall I32, one duct I35 atthe center and the other duct I 37 toward the edge of the wall I32.Between the lower ends of these ducts in a spiral groove I38 cut intothe interior surface of the wall I32, a three turn spiral being shown.The material to be treated enters through either one of the ducts I36and I31, flows around the spiral, and leaves through the other duct. Theconcentrated ultrasonic energy passes through the diaphragm I34 andeffects treatment along the entire spiral course of fiow.

An additional alternative form of the treatment head is illustrated inFig. 10. In this figure also a head, designated MI, is fastened so thatit opens directly into the casing I9 of Fig. 4 without the interpositionof a diaphragm, sealing being obtained with the washer H3. Near the topof the treatment chamber a circular abutment I42 carries a smalldiaphragm I 43. The head MI resembles in some respects the head 23 ofthe Fig. 1 device, since the head I II also has a concentric arrangementof an outer pipe I44 and an inner pipe I 46 to permit concentric flow ofthe material to be treated while entering and leaving the head. Thus thematerial may flow through the annular space between the pipes I44 andI46 into a small region I41 above the diaphragm I43. In the region I41the material is subjected to the concentrated acoustic energy in thefocal region of the device. Thereafter the treated material leavesthrough the central pipe I46. An additional entrance duct I43communicates from the side with the treatment region I41, permitting oneliquid to be introduced through this duct and emulsified in the regionI4! with another liquid introduced through the aforementioned annularspace, between the pipes I44 and I46. The short, direct flow paths andthe small size of the region I41 make possible rapid and completetreatment of the liquid or liquids entering the head I4I.

Still another type of treatment head is illustrated in Fig. 11. Thishead designated II, also is designed to be substituted for head III ofthe Fig. 4 arrangement. A diaphragm H2 is inserted between the housingI9 and the washer I I3. The diaphragm I I2, however, bulges rathersharply upward toward the center of the head I5I, as shown in Fig. 11.

Material to be treated in the head illustrated in Fig. 11 enters througha pipe, shown schematically at I52, connecting with an inlet duct I53entering the upper part of the interior of the head I5I. An outlet pipeI54 communicates with the interior of the head I5I through the center ofthe upper wall of the head and tapers toward a constricted throat I55near the center of the head. To the bottom of this throat is brazed awidely flared continuation I5? of the outlet pipe I54. The flared memberI5? conforms roughly to the configuration of the diaphragm IIZ, leavinga rather narrow space between the diaphragm and the inside of the flaredstructure I51.

Material to be treated in the head illustrated in Fig. 11 flows into thetop of the head, down to the bottom of the interior space near the outerwalls thereof, and thence between the diaphragm H2 and the flaredstructure I51. In the region near the throat I58 of the outlet pipe I54the material is subjected to intensive acoustic irradiation while beingconfined closely to a small region of greatest energy concentration.

With reference to the operation of the Fig. 4 device when equipped withthe head I5I of Fig. 11, the acoustic energy is transmitted into theliquid medium 2I which is within the housing I9 and in contact with theelectro-acoustically responsive radiator or array mounted at the bottomof the housing. The diaphragm II2 constitutes a solid acoustic energybarrier remote from the radiator and separating the liquid medium 2Ifrom the focal region Within the treatment head. The pressure chamberI52 of the Fig. 4 arrangement may be adjusted to maintain the liquid 2|under a substantial hydrostatic pressure within the housing I9 andcontiguous to the lower side of the barrier or diaphragm I I2. Thearrangement of the head I5I of Fig. 11 constitutes a preferred form ofmeans for directing a flow of a liquid material to be treated through afocal region of small volume so as to subject all of the materialexpeditiously to acoustic treatment.

The inlet and outlet pipes I52 and I54 are shown broken in Fig. 11 toindicate that they may extend vertically a substantial distance abovethe top of the head I5I in order to maintain the liquid material in thefocal region and contiguous to the upper side of the diaphragm II2 undera substantial hydrostatic pressure. These provisions for maintaininghydrostatic pressure within the housing I9 proper and also within thetreatment head result in increasing the level of acoustic energyintensity which may be attained without the flow of this energy beinginterrupted by excessive cavitation. Ordinarily the intensity, thepressures, and the rates of flow are adjusted to achieve cavitation onlyin a small region in the center of the head I5I, near the throat I56 ofthe outflow pipe. Cavitation takes time to develop, and increasing therate of flow of a liquid through a region of high acoustic energyintensity delays or avoids the onset of cavitation, particularly whenthe flow is in the same direction as the direction of propagation of theacoustic waves.

Fig. 12 shows another form of the focused treatment device. As with thedevices of Figs. 1 and 4, a base II" is provided for mounting a supportmember I3 at the edge thereof by means of the screws 34, 35. The baseII, however, is more deeply recessed to provide a rather large clearancebetween the inside of the base and the support I3. A single centrallylocated boss 38" helps to brace the support I3. The arrangement of thetransducer itself is the same as in Fig. 4. Sensitive elements I5, IE,IT, etc. are fastened to the support I3. Electrical energy of acousticfrequencies at high power levels is introduced through a cable 6|, ofwhich one conductor is grounded to the lug 62' on the connector 63' andthe other conductor passes through the connector to the internal bus 66.

A unitary housing and duct member I9" has a generally conical shape witha flanged portion at the larger end which is fastened to the base II" bymeans of the bolts 28, 29. The compression ring 21 seals the joint. Thesmaller end of the housing I9 has a rather narrow throat portion I6I,and then broadens somewhat to form a duct portion I62 for receiving asuitable connector fitting, not shown, for handling the liquid to betreated. Another fitting I53 is provided near the center of the base II.Two small auxiliary inlet ducts I64 and I55 enter the housing I9" nearthe constricted region I6I.

Although illustrated with its axis vertical and with theelectro-acoustically responsive array at the bottom, the Fig. 12 devicemay be used in other positions, notatably with its axis vertical butwith the array at the top and the throat I5I at the bottom. The array,on the concave supporting surface of the support member IS, in the Fig.12 device does not direct acoustic energy toward a predetermined focalregion on the remote side of an acoustic-energy-transmitting wallportion such as the wall 25 of Fig. 1 or the diaphragms of the treatmentheads in Figs. 4-11. Instead, in the device shown in Fig. 12, the arraysimply directs the acoustic energy toward a predetermined focal regionwithin the open interior of the housing I9" near the throat I6I. Thus,the acoustic energy of high intensity in the focal region, instead ofbeing transmitted through a wall or other barrier, passes without anybarrier whatever through a liquid 2 I within the housing I9".Undesirable internal reflections may be prevented by forming the housingl8" sothat it tapers smoothly in cross-sectional area toward theconstricted portion lSi bordering the focal region.

lathe Fig. 12 arrangement the acoustic medium itself the liquid to betreated. Means areprovided communicating with the space between the baseI I and the support l3, for passing the liquid to be treated, forexample an aqueous liquid, from the back surface of the support memberl3 through the perforations therein, past the elements l5, l6, etc., andthrough the focal region within the constricted portion IQ! of thehousing [9", wherein acoustic energy translated from the array to theaqueous liquid in contact with the array is focused for high intensityacoustic treatment of the same liquid within the constricted portion Islof the hqu nsi When an aqueous liquid is to be treated, it isadvantageous to employ sensitive elements of the Water-insolublepolycrystalline titanate-type material to avoid attack upon the elementsby the liquid to be treated. With pro er design it is practical tooperate the Fig. 12 arrangement with the elements under water. Anultrasonic frequncy of the order of 500 kilocycles per second isrecommended. It is understood then that the elements will becorrespondingly shorter and narrower to permit operation in longitudinalmode resonance without interfering resonances in other modes. Theimpedance of the elements, due to their very high permittivity, is solow that the shunting impedance of the aqueous material between theelectrodes may be almost negligible, This combination of ability towithstand water, high electromechanical response, and low impedance makethe titanate-type elements extraordinarily useful. A further advantageof the low. impedance is, that large amounts of power can be used todrive the. elements and produce acoustic fields of high intensitywithout necessitating the application of high voltages. Voltages of theorder of 100 volts R. M. S. ordinarily are sufiicient with prepolarizedbarium titanate bodies.

While it, is difficult to obtain effective waterproofing without bulkycoverings, it may be desirable to decrease the shunting effect. of anaqueous liquid on the array by applying coatings of plastic or othermaterials having high electrical resistance to. the titanate-typeelements and thelead conductors connected thereto. Any seepage ofmoisture through such a coating will not damage the water-insolubleelements, and the insulating properties of the coating will remainsufficiently unimpaired to permit the use of lower ultrasonicfrequencies without, intolerable shunting of the electric energy throughthe aqueous liquid around the array.

If desired the material may flow into the Fig. 12 device at the duct endI62 of the housing l9" and out through the fitting I63, It is preferred,however, to have the flow in the other direction, as describedhereinabove. Substantial advantages also may accrue from directing theacoustic energy vertically downward, the apparatus being disposed withthe throat l6| of the housing at the bottom of the device. With thisdisposition of the device heavy materials may be treated when onlycrudely suspended in a liquid medium. Any solid particles coming out ofsuspension, whether or not agglomerated during the treatment, must falltoward the treatment region near the throat [6| instead of settlingaround the radiating array. Eurthermore, some treatment P e s e ui e u eOf ather Small q 'a tities of liquid or solid materials which do not mixor dissolve in the main body of the liquid medium and which havechemical or physical properties which might cause damage to thetransducer assembly. In such a case the injurious material may beintroduced through the auxiliary ducts I64 and I66 near the throat IBI.If such materials tend to settle downward, it is advantageous to use theFig. 12 device in the inverted position, so that the injurious materialsdo not settle toward the array.

While there have been described what at present are considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without deg parting from the invention. It is aimed, thereefore, in the appended claims to cover all such changes and modificationswhich fall within the true spirit and scope of the invention.

What is claimed is:

l. A focused acoustic treatment device comprising: electromechanicaltransducing means for directing acoustic energy from anelectroacoustically responsive radiator of sizable. area toward a focalregion having high acoustic energy intensity, having a relatively smalleffective area, and having a correspondingly small volume; a liquidacoustic transmission medium in contact with said radiator; a solidacoustic-energytransmitting barrier remote from said radiator andseparating said liquid medium from said focal region; and means fordirecting a flow of a liquid material to be treated into said device andthrough said focal region of small volume and for maintaining saidliquid material under a substantial hydrostatic pressure to. subjectsubstantially all of said material in said. flow expeditiously to saidacoustic energy ofhigh intensity.

2. A focused acousticv treatment device comprising: electromechanical.transducing means for directing acoustic energy. from anelectroacoustically responsive radiator of sizable area toward a focalregion having high acoustic energy intensity, having a relatively smallelfective area, and having a correspondingly small v01 ume; a liquidacoustic transmission medium in contact with said radiator; a housingfor said radiator and said liquid medium; a solid acous for maintainingsaid liquid medium under a sub stantial. hydrostatic pressure withinsaid housing and. contiguous to one side of said barrier; andmeans fordirecting a flow of a liquid material to be treated into said device andthrough said focal region of small volume and for maintaining saidliquid material in said focal region and contiguous to the other side ofsaid barrier under a substantial hydrostatic pressure to subjectsubstantially all of said material insaid flow expeditiously to saidacoustic energy of-high intensity. 7 v

3. An electromechanical device for transducing from electrical energy toacoustic energy propagating in a fluid acoustic medium compris ing: asupport member having a back surface and an opposed supporting surfaceand having numerous perforations therethrough; acousticpressure-releasing means afiixed on one side thereof to said supportingsurface and having numerous openings at least partially aligned-withsaid perforations; a plurality of electromechan ,acsaesa icallysensitive elements, each having a back surface, afiixed to saidpressure-releasing means on the other side thereof, and a front surface,said front surfaces collectively forming an electro-acousticallyresponsive array for coupling to said fluid acoustic medium; and means,including electrodes adjacent to each of said elements and a system ofleads connected to said electrodes, for applying electrical energy tosaid electro-acoustically responsive array; said transducing devicebeing arranged for motion of said fluid acoustic medium from said backsurface of said support member through said perforations and past saidelements during operation of said device.

4. An electromechanical device for transducing from electrical energy toacoustic energy propagating in a fluid acoustic medium comprising: asupport member having an electrically conductive back surface and anopposed supporting surface and having numerous perforationstherethrough; acoustic pressure-releasing means affixed on one sidethereof to said supporting surface and having numerous openings at leastpartially aligned with said perforations; a plurality ofelectromechanically sensitive elements, each having a back surface,affixed to said pressure-releasing means on the other side thereof, anda front surface, said front surfaces collectively forming anelectro-acoustically responsive array for coupling to said fluidacoustic medium; electrodes adjacent to said back surface and to saidfront surface of each of said elements; lead conductors passing throughsaid perforations and connecting said conductive back surface of saidsupport member with said electrodes adjacent to said back surfaces ofsaid elements; lead means arranged in proximity to said front surfacesof said elements and interconnecting said electrodes adjacent to saidfront surfaces; and terminal-circuit means for applying electricalenergy across said lead conductors and said lead means; said transducingdevice being arranged for motion of said fluid acoustic medium from saidback surface of said support member through said perforations and pastsaid element during operation of said device.

5. An electromechanical device for transducing from electrical energy toacoustic energy propagating in a liquid acoustic medium comprising: asupport member having a back surface and an opposed supporting surfaceand having numerous perforations therethrough; acousticpressure-releasing means affixed on one side thereof to said supportingsurface and having numerous openings at least partially aligned withsaid perforations; a plurality of electromechanically sensitive elementsof polycrysta1 line titanate-type material, each having a back surface,affixed to said pressure-releasing means on the other side thereof, anda front surface, said front surfaces collectively forming anelectro-acoustically responsive array for coupling to said liquidacoustic medium; and means, including electrodes adjacent to each ofsaid elements and a system of leads connected to said electrodes, forapplying electrical energy to said electro-acoustically responsivearray; said transducing device being arranged for motion of said liquidacoustic medium from said back surface of said support member throughsaid perforations and past said elements during operation of saiddevice.

6. An electromechanical device for transducing from electrical energy toacoustic energy propagating in a liquid acoustic medium comprising: asupport member havinga back surface and an opposed supporting surfaceand having numerous perforation therethrough; acousticpressure-releasing means afiixed on one side thereof to said supportingsurface and having numerous openings at least partially aligned withsaid perforations; a plurality of electromechanically sensitiveelements, each having a back surface, affixed to said pressure-releasingmeans on the other side thereof, and a front surface, said frontsurfaces collectively forming an electro-acoustically responsive arrayfor coupling to said liquid acoustic medium; means, including electrodesadjacent to each of said elements and a system of leads connected tosaid electrodes, for applying electrical energy to saidelectro-acoustically responsive array; and means for maintaining saidliquid medium, acoustically coupled to said array, under a substantialhydrostatic pressure; said transducing device being arranged for motionof said pressurized liquid acoustic medium from said back surface ofsaid support member through said perforations and past said elementsduring operation of said device.

'7. An electromechanical device for transducing from electrical energyto acoustic energy propagating in a liquid acoustic medium comprising: asupport member having a back surface and an opposed supporting surfaceand having numerous perforations therethrough; acousticpressure-releasing means aflixed on one side thereof to said supportingsurface and. having numerous openings at least partially aligned withsaid perforations; a plurality of electromechanically sensitiveelements, each having a back surface, afiixed to said pressure-releasingmeans on the other side thereof, and a front surface, said frontsurfaces collectively forming an electroacoustically responsive arrayfor coupling to said liquid acoustic medium; means, including electrodesadjacent to each of said elements and a system of leads connected tosaid electrodes, for applying electrical energy to saidelectro-acoustically responsive array; and means for degassing saidliquid medium while acoustically coupled to said array during operationof said transducing device; said transducing device being arranged formotion of said liquid acoustic medium from said back surface of saidsupport member through said perforations and past said elements duringoperation of said device.

8. An electromechanical device for transducing from electrical energy toacoustic energy propagating in a liquid acoustic medium comprising: ahousing having a wall portion adapted to transmit acoustic energy; asupport member affixed to said housing, having a back surface and anopposed supporting surface, and having numerous perforationstherethrough; acoustic pressure-releasing means affixed on one sidethereof to said supporting surface and having numerous opening at leastpartially aligned with said perforation; a plurality ofelectromechanically sensitive elements, each having a back surface,afiixed to said pressure-releasing means on the other side thereof, anda front surface, said front surfaces collectively forming anelectro-acoustically responsive array directed toward saidacoustic-energy-transmitting wall portion; means, including electrodesadjacent to each of said elements and a system of leads connected tosaid electrodes, for applying electrical energy to saidelectro-acoustically responsive-array; and liquid-guiding means fordirecting a flow of said liquid :acous'tic medium at a substantialvelocity from said back surface of said support member through saidperforations, past said elements within said housing toward said wallportion thereof, and thence generally laterally of said wall portion toestablish a continuous acoustic path through said moving liquid mediumbetween said array and said acoustic-energy-transmitting wall portion.

9. .An electromechanical device for transducing from electrical energyto acoustic energy propagating in a liquid acoustic medium comprising:ahousing having a wall portion adapted to transmit acoustic energy; asupport member affixed to said housing, having a back surface and anopposed supporting surface, and having numerous perforationstherethrough; acoustic pressure-releasing means affixed on one sidethereof to said supporting surface and having numerous openings at leastpartially aligned with said perforations; a plurality ofelectromech'anically sensitive elements, each having a back surface,affixed to said pressure-releasing means on the other side thereof, anda front surface, said front surfaces collectively forming an:electro-acousticallly responsive array directed toward *saidacoustic-energy-transmitting wall portion; means, jincluding'electrodesadjacent to each of said elements and a system of leadsconnected "tosaid :electrodes, for applying electrical energy to said;electr.o-:acoustically responsive array; liquid-guiding means forcirculating said liquid acoustic medium "at a substantial velocity fromsaid back surface *of said support member through said perforations,past said elements within said "housing toward said wall portionthereof, and thence igenerally laterally of said wall portion andreturning to said back surface of said support member; and means formaintaining said circulating liquid medium under a substantialhydrostatic :pressure while between said array and said acousticenergy-transmitting'wall-por'tion and for continuously degassing saidliquidrmedium, whereby ;a continuous acoustic path is establishedthroughsaid pressurized, degassed moving :liquid medium between said array andsaid wall portion.

10. focused acoustic treatment device comprising: a housing having :a:wall portion adapted to ztransmitacoustic energy; :a support memberaffixed .to :said housing, having a back surface and an opposedruoncavesupporting surface, and having numerous perforations therethrough;acoustic pressure-releasing means afiixed one one side'thereof to saidconcave supporting surface and having numerousopenings atleast-partially aligned with said perforations; a plurality ofelectromechanically sensitive elements, "each having a backsurfacaaiiixed to said pressurereleasing means on the other sidethereof, and a front surface, said front surfaces collectively formingan electro-acoustically responsive array for directing acoustic :energytoward :a predetermined .focal'region on the remote sideof said acousticenergy transmitting wall portion; means, including electrodes adjacentto each of said elements and-a system of leads connected to saidelectrodes, for-applying electrical energy to .said electroeacousticallresponsive array; a liquidracoustic vtransmissionzmediuni within saidhousing; liquid-guiding vmeans for directing a flow of saidliquidacousticmedium .at a substantial'velo'city from said back surface ofsaid support member through said perforations, "past said "elementswithin-said housing "toward said wall portion thereof, and thencegenerally lat erally of said wall portion to establish a continuousacoustic path through said moving liquid medium between said array andsaid acoustic-energy-transmitting wall portion; and means for directinga flow of material to be treated into said device on said remote side ofsaid wall portion and through said focal region to subject substantiallyall of said material in said flow expeditiously to acoustic energy ofhigh intensity transmitted through said wall portion to said focalregion.

11. A focused acoustic device for treating liquids comprising: a supportmember having a back surface and an opposed concave supporting surfaceand having numerous perforations therethrough; acousticpressure-releasing means affixed on one side thereof to said concavesupporting surface and having numerous openings at least partiallyaligned with said perforations; a plurality of electromechanicallysensitive elements, each having a back surface, afiixed to saidpressure-releasing means on the other side thereof, and a front surface,said front surfaces collectively forming an electro-acousticallyresponsive array for directing acoustic energy toward a predeterminedfocal region; means, including electrodes adjacent to eachofsaid .ele-.-ments, for applying electrical energy to said elec tro-acousticallyresponsive array; ahousing containing said support member and having aportion of constricted cross-sectional area bordering said focal region;and means for passing 'liqr uid to be treated from said back surface ofsaid support member through said perforations, past said elements, andthrough said focal region within said constricted portion of saidhousing, wherein acoustic energy translated from said array to saidiliquid is focused .for'high intensity acoustic treatment vof saidliquid.

12. A :focused acoustic device for treating liquids comprising: asupport member having a back surface and an opposed concave supportingsurface and having numerous perforations-therethrough; acousticpressure-releasing means affixed on one side thereof to said.concavesupporting surface and having numerous openings at .leastpartially aligned with said perforations; a plurality 'of'electromechanically sensitive elements, each having .a back surface,-.afiixed to said pressure-releasing means on the other sidethereofandafrcnt surface, said front surfaces collectively forming anelectroeacoustically respcnsive array for directing acoustic energytoward :a predetermined focal region; means, .including electrodesadjacent toeach of said elements, for applying-electrical energy to-saidelectro-acousticaily responsive array; a'housing containing :saidsupport member and tapering in internal cross-sectionalarea toward aconstricted portion bordering said focal region; and means for passingliquid to be treated from said'back surface of .said support memberthrough said perforations, past said elements, and :through said focalregion withintsaid constricted portion of :said housing, wherein lacoustic energy translated'vfrom .said .array to said. liquid is focusedfor high intensity acoustic treatment of said liquid.

13. A focused acoustic device for treating liquids comprising: a supportmember havinga back surface and an opposed concave supporting surfaceand havin numerous perforationstherethrough; acoustic pressure-releasing-means af- "fixed on one side thereof to said concave supporting surfaceand having numerous openings at least partially aligned with saidperforations; a plurality of. electromechanically sensitive elements ofpolycrystalline titanate-type material, each having a back surface,afiixed to said pres,- sure-releasing means on the other side thereof,and a front-surface, said front surfaces collectively forming anelectro-acoustically responsive array for directing acoustic energytoward a predetermined *focal region; means, including electrodesadjacent to each of said elements, for applying electrical energy tosaid electro-acoustically responsive array; a housing containing saidsupport member and having a portion of constricted cross-sectional areabordering said focal regiongiand means for passing liquid to be treatedfrom, said back surface of said support member through saidperforations, past said elements, and through said focal region withinsaid constricted ,portion of said housing, wherein acoustic energytranslated from said array to said liquid isifocused for high intensityacoustic treatment of;said liquid.

14. A focused acoustic device for treating liquids comprising: a supportmember havinga back surfaceifand an opposed concave supporting surfaceand having numerous perforations therethrough; acousticpressure-releasing means affixed on one;,side thereof to said concavesupporting surface and having numerous openings at least partiallyaligned with said perforations; a plurality of electromechanicallysensitive elements of water-insoluble polycrystalline titanate-typematerial, each having a back surface, aflixed to said pressure-releasingmeans on the 26 other side thereof, and a front surface, said frontsurfaces collectively forming an electro-acoustically responsive arrayfor directing acoustic energy toward a predetermined focal region;means, including electrodes adjacent to each of said elements, forapplying electrical energy to said electro-acoustically responsivearray; a housing containing said support member and having a portion ofconstricted cross-sectional area borderin said focal region; and meansfor passing an aqueous liquid to be treated from said back surface ofsaid support member through said perforations, past said elements, andthrough said focal region within said constricted portion of saidhousing, wherein acoustic energy translated from said array to saidaqueous liquid in contact with said array is focused for high intensityacoustic treatment of said liquid within said constricted portion ofsaid housing.

ALFRED L. W. WILLIAMS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,163,650 Weaver June 27, 19392,251,959 Smith Aug. 12, 1941 2,438,936 Mason Apr. 6, 1948 2,514,080Mason July 4, 1950 FOREIGN PATENTS Number Country Date 654,673 GermanyDec. 24, 1937

